public class code2 {
    public ListNode FindKthToTail (ListNode pHead, int k) {
        //边界情况
        if(pHead == null) return pHead;
        //快慢双指针
        ListNode fast = pHead;
        ListNode slow = pHead;
        //先让fast走k步
        while(k--!=0) {
            if(fast == null) {
                return null;
            }
            fast = fast.next;
        }
        //slow和fast一起走
        while(fast != null) {
            fast = fast.next;
            slow = slow.next;
        }
        return slow;
    }
}
